The embodiments of the present invention relate to the field of surface permanent magnet electric machine control, in particular to a method for on-line estimation of an initial position of a surface permanent magnet electric machine in a stationary state or at a first speed, and an apparatus for on-line estimation of an initial position of a surface permanent magnet electric machine in a stationary state or at a first speed.
To drive a surface permanent magnet synchronous electric machine (SPMSM/SPM: Surface Permanent Magnet Synchronous Motor), it is necessary to acquire rotor position in order to realize vector control (FOC: Field Oriented Control). Without a rotor position sensor, rotor position can be estimated by extracting position information from measured phase currents. When the synchronous electric machine is operating at zero speed or at a low speed (generally 10% of the rated speed), the back emf is very small because the speed is also very small. In such a situation, a method of High Frequency Pulsating Voltage Injection (HFPVI) is generally used to extract rotor position information.
In principle, the HFPVI method only tracks the position of a rotor salient pole; this position does not include rotor position polarity. If the estimated rotor position polarity is not accurate, then electromagnetic torque will be opposite to reference torque, and this will lead to failure of pole control. A prior method for estimating rotor position polarity is to inject voltage pulses from positive and negative directions of the d-axis respectively and determine rotor polarity according to a measured current amplitude difference. However, the method requires the injection of voltage signals at least twice, and a long time (of the order of hundreds of milliseconds) must be consumed before rotor polarity is determined; moreover, the method must determine rotor polarity when the pole is in a stationary state. Thus, such a method is an off-line method, and so cannot be used for starting an electric machine having a certain initial speed.